FIGS. 18A and 18B are a schematic drawing and an overhead view for explaining a light emitting diode assembly in the form of a light emitting device of the prior art having a light emitting diode as the light source thereof. In FIGS. 18A and 18B, a light emitting diode assembly 60 is composed of a printed wiring board 61, a submounting substrate 62 provided on the printed wiring board 61, a plastic hollow body 63 surrounding the periphery of the submounting substrate 62, a light emitting diode 65, and a transparent sealing resin 66 covering the light emitting diode 65.
The plastic hollow body 63 is integrally molded with a lead frame 64 by a thermosetting resin having an epoxy resin as a main component thereof. The printed wiring board 61 has printed wires 611 for connecting with a control circuit not shown for operating the light emitting diode 65 formed in a desired pattern by etching and the like. The submounting substrate 62 has a pair of wires 622 formed in the upper surface thereof by forming a vapor deposition pattern using etching or a mask.
In the plastic hollow body 63, the lead frame 64 passes through a sidewall. The plastic hollow body 63 is integrally produced by so-called insert or outsert molding (injection molding) in which a portion of the lead frame 64 is embedded therein during molding. The plastic hollow body 63 reflects light emitted by the light emitting diode 65 with the surface of an inner wall thereof.
The light emitting diode 65 is provided with two electrodes 623 at the bottom, is cut out from a semiconductor wafer by dicing, and has the electrodes 623 connected to the wires 622 of the submounting substrate 62.
The transparent sealing resin 66 has heat resistance, is filled into the plastic hollow body 63, and comprises a flat or convex lens.
FIGS. 19A and 19B are a cross-sectional view and overhead view for schematically explaining a light emitting device of the prior art having for a light source thereof a vertical geometry light emitting diode, and FIG. 19C is a schematic drawing for explaining a vertical geometry light emitting diode. A light emitting device 51 of the prior art shown in FIGS. 19A and 19B is composed of metal substrates 53 and 54, a slit 55 located between the metal substrates 53 and 54 (in some cases, a filling material is filled therein), a vertical geometry light emitting diode 52 attached to one metal substrate 53, gold wires 511 and 512 for connecting another metal substrate 54 with an upper electrode 523 of the vertical geometry light emitting diode 52, a reflector 56, a transparent sealing resin 57 filled into an opening surrounding the vertical geometry light emitting diode 52 in the reflector 56, and a fluorescent material-containing film 58 provided on the upper portion of the reflector opening, and connection between the metal substrate 54 and the upper electrode 523 of the vertical geometry light emitting diode 52 is made by wire bonding using the gold wires 511 and 512. As shown in FIG. 19A, the reflector 56 is composed of a nearly cylindrical body having an opening comprising a reflecting portion inclined so as to spread upward.
As shown in FIG. 19C, the vertical geometry light emitting diode 52 is at least composed of a lower electrode 521, a light emitting layer 52′ formed above the lower electrode 521, a transparent conductive film 522 formed above the light emitting layer 52′, and an upper electrode 523 formed on the transparent conductive film 522.
In the light emitting diode package described in JP 2001-244508 A, a lower electrode of a vertical geometry light emitting diode is attached to one metal substrate, while an upper electrode of the vertical geometry light emitting diode is connected to another insulated metal substrate with bonding wires.
In a light emitting diode package of the prior art, a resin is inserted into an insulated portion of a metal core. A production method for this type of light emitting diode package is described in, for example, JP 2005-116579 A.
A known example of a light emitting device that uses a surface-mounted light emitting diode is a light emitting device in which a submounting substrate in which a light emitting diode is sealed with a sealing resin is mounted on separate metal core substrates with an insulating adhesive. A light emitting device that uses this type of surface-mounted light emitting diode as a light source is described in, for example, JP 2003-303999 A.
Flip chip light emitting diodes of the submounted type offer the advantage of allowing all emitted light to be radiated to the outside since they do not have an electrode in the upper portion thereof.
On the other hand, vertical geometry light emitting diodes have been developed in recent years that have superior performance to flip chip light emitting diodes. In contrast to vertical geometry light emitting diodes allowing a larger current flow and improved luminosity, since configurations of the submounted type have difficulty in dissipating heat generated from the light emitting diode due to poor thermal conductivity, the package easily reaches a high temperature thereby resulting in the disadvantages of wiring disconnections occurring during the course of use or failure of the light emitting diode itself. In addition, submounted types also had the problem of poor productivity.
Vertical geometry light emitting diodes have come to be larger, demonstrate better emission efficiency and yield higher luminosity.
In light emitting devices of the prior art having for a light source thereof a vertical geometry light emitting diode, the upper electrode of the light emitting diode and a metal substrate are connected by wire bonding as previously described. The gold wires used for wire bonding are connected to the upper electrode of the vertical geometry light emitting diode by thermocompression and ultrasonic oscillation by, for example, a robot (automated special-purpose machine). Consequently, in the case of connections by bonding using gold wires, vibrations and pressure generated impart a stimulus to the semiconductor layer and light emitting layer of the upper portion of the vertical geometry light emitting diode through the upper electrode, possibly resulting in damage thereto. Consequently, it is necessary to subtly adjust the pressure and ultrasonic oscillation of the wire bonder to prevent damage to the semiconductor layer and light emitting layer of a vertical geometry light emitting diode caused by vibrations and pressure, resulting in a tendency for an increase in the connection resistance of the gold wires.
However, it was necessary for further increase the flow of current to increase the luminance of light emitting diodes. In this case, since there are limitations on how much the diameter of gold wire can be increased, a plurality of wires were used to increase current capacity. Even if a plurality of gold wires are used, since greater heat is generated from the gold wires when current capacity is increased, adhered portions became defective over the course of time. In addition, when a large current is allowed to flow through gold wires connecting the upper electrode of a vertical geometry light emitting diode attached to one substrate and another substrate, thermal stress occurs due to the generation of heat, thereby resulting in the problem of disconnections or causing the vertical geometry light emitting diode to burn out due to the resistance at connection of gold wire with the upper electrode or the substrate.
Moreover, light emitting devices of the prior art having as a light source thereof a vertical geometry light emitting diode are not only susceptible to the occurrence of connection defects over time with respect to providing a plurality of gold wires, but also had the problem of poor productivity attributable to an increase in the number of production steps and the need to subtly adjust the pressure and ultrasonic oscillation of the wire bonder.